Commercial Image Quality Test Lab Setup

At Imatest, we help you decide what to consider when setting up an image-quality lab, including products and services that ensure accurate and reliable measurements as well as general guidelines for configuring a commercial image-quality lab suitable for pre-production validation of imaging systems. Read through important considerations before you begin testing, or walk through the guidelines for a proper test lab setup.

View this video to see how FOV impacts the charts and environment you need for your imaging lab.

To select an appropriate test chart size, you need to know the pixel dimensions (width and height) of your sensor, diagonal FOV of your lens, and ideal lens-to-chart distance. Enter these details into the Imatest Chart Finder to determine the size of your imaging plane and identify the ideal chart.

Figure 1: SFRreg charts outside of an eSFR ISO resolution test chart.

Wide FOV typically ranges between 100º and 160º and has fixed-focus distances closer than normal. The lens-to-chart distance is commonly between 18cm and 1m. Predistorted charts are the best solution for testing wide FOV, such as those captured by fisheye lenses. These charts are designed with pincushion distortion to correct for the lens’ barrel distortion so features within the captured image will be as rectilinear as possible.

Ultrawide cameras with a FOV greater than 160º are increasingly common but can be challenging to test. For example, it is difficult to fill the image plane with a planar test chart even with pincushion pre-distortion. To solve this problem, place SFRreg charts outside of an eSFR ISO resolution test chart (Figure 1). The Imatest software eSFR ISO module will automatically detect these charts for analyzing sharpness and chromatic aberration.

The Imatest Ultrawide Test Fixture is designed to provide an out-of-the-box solution to align charts properly for measuring sharpness and chromatic aberration. It works with cameras with FOV up to 180° at 1m or 270° at 50cm lens-to-chart distance. For testing ultrawide uniformity, a spherical light source becomes necessary to fill the FOV and avoid the cosine-falloff that will be present on a flat-panel light source.

Long range and narrow FOV testing

Testing narrow FOV lenses, where the focusing range may cover between 5m and up to hundreds of meters, can be costly and complicated to achieve in most imaging labs. When testing requirements extend beyond your available space, collimating optics can produce virtual images at or beyond the hyperfocal distance.

If you are interested in testing narrow FOV lenses, Imatest offers custom solutions for testing long distances within a compact environment. Contact us for more information about simulating long distances.

Test distances

At a minimum, you should make sure to test beyond your minimum focus distance. However, determining the appropriate test distances depends on your device’s application. It may only be necessary to test your camera system beyond the hyperfocal distance to ensure it is acceptably sharp for far away objects. Alternatively, you may require multiple test distances, such as one close to the minimum focus distance and another beyond the hyperfocal distance.

The test chart is what Imatest software uses to measure the quality factors of your imaging system. It is important to take great care of your test charts. Always handle your test chart with clean, white cotton gloves to keep it free from blemishes and dirt. Be careful not to drop or fold charts as that can cause irreparable damage. For more information on test chart care and store, please see the section on chart mounting below.

Lighting Considerations

Glare-free, uniform illumination on your test chart is necessary for Imatest software to measure the quality of your system accurately and can be achieved using reflective or uniform light sources.

When selecting light sources, consider ones with high uniformity to ensure accurate chart readings (refer herefor the effects of non-uniform lighting on sharpness measurements). Integrated dimming capabilities can be useful when measuring imaging system quality across different levels of light to simulate multiple real-world scenes.

Uniformity

Uniformity measurements indicate an imaging system’s tendency to become darker the farther away from the center of the image. This occurrence is due to the radial nature of the lens which collects more light in the center and can be particularly strong with wide angle lenses. Testing for uniformity requires light sources with the highest uniformity levels possible. Imatest Lightboxes and Light Panels are available with 90% uniformity or 95% for sizes A through C (an option for the Light Panels), which is sufficient for most devices. If you are testing uniformity for an ultrawide camera, you will need to use a spherical light source because a flat-field light source will not completely fill the FOV in order to test the uniformity of the whole sensor.

Reflective Lighting

Reflective test charts can test most image quality factors. High illumination reflective light sources are required for accurate chart measurement. The vertical orientation of our reflective lighting options keeps light levels consistent from the bottom to the top of the test chart. For a more detailed overview of reflective lighting qualities, see our Reflective Lighting page.

Transmissive Chart Lighting

Transmissive chart lighting provides a solution for ultra-high resolution and dynamic range testing. For accurate analysis, transmissive charts need to be placed on a uniform, backlit light surface (such as a lightbox or light panel). A highly uniform light source allows you to test the uniformity of your camera. Imatest offers a variety of uniform light sources, including the Imatest LED Light Panel which is compact and portable, has integrated chart mounting, and features wireless controls. For dynamic range and ultrahigh resolution testing, the Imatest LED Lightbox with a high-precision film chart is better suited. It has high-uniformity levels of 90% to 95% and comes in a wide range of sizes (shown below) and intensities.

Test Lab Setup

Now that you understand the key factors for successful lab setup, here’s how to put it all together.

Environment

To obtain precise measurements, your lab setup should be in a space with as little ambient lighting as possible, such as an interior, windowless room. Walls should be painted neutral middle gray (N5) to black, using a matte, flat, or eggshell wall paint to minimize reflected light. Reflective surfaces, such as polished metal or white/light colored surfaces, should be minimized. All additional light sources, including room lights, windows, doorways to other rooms, and LED indicators on equipment, should be covered or eliminated while conducting tests.

To ensure the most accurate and repeatable results, use a professionally mounted chart and a chart-mounting system that enables precise alignment of your chart and lens. Charts should be mounted horizontally unless otherwise specified to ensure Imatest software recognizes the chart. Check that your chart and camera system are each level relative to one another. The chart does not need to be level with the ground if it is level with the device. If your environment allows, it is acceptable to test your device pointed down with the chart on a floor or table; e.g. with a microscope.

Imatest offers many solutions for setting up test charts. Options include manual mounting, utilizing a modular system, quickly switching between charts with robotic automation, or testing with nonplanar targets at predefined locations.

The Modular Test Chart Mounting System offers great efficiency and versatility. Available in a range of sizes, the panel consists of a steel surface with neutral gray (N5) enamel matte finish, to which charts can be easily mounted using magnets.

The Automatic Test Chart System uses robotics for the automatic placement of test charts into the imaging plane, offering quick interchangeability between many charts at the touch of a button.

It is strongly recommendedthat charts be mounted on a smooth flat surface, like an acrylic board, to ensure no blemishes, bends, or bubbles occur that would negatively impact image quality measurements. Imatest offers the option to professionally mount our test charts on acrylic or ePanel (as shown above) for additional shipping and handling fee—contact sales for more information about this service.

Lighting

Arrange your lighting equipment for even, glare-free illumination. Lighting angles should be between 35° and 45°, as shown in Figure 2. Avoid placing the lighting behind the lens or at angles greater than 45° as that can cause glare and cast shadows on the test chart. Angles less than 20° can cause issues with texture and lighting uniformity. It is beneficial to have light modifiers to reduce flare light. Orienting your reflective light fixtures vertically allows for even illumination by keeping light levels consistent from the bottom to the top of the test chart.

Addressing glare

Matte charts are best suited for avoiding glare under most test scenarios. Glare in the outer patches of your test chart can ruin measurements and is hard to avoid with semigloss charts. If you must use semigloss charts, reduce glare by decreasing the angle between the lights and the chart, but be sure to verify your illumination levels remain consistent. If you’re not sure whether your testing needs can be met with a matte chart, or need help troubleshooting glare, contact Imatest.

Lighting uniformity requirements

When setting up your lab, verify lighting uniformity. Lighting uniformity is strongly affected by the distance and orientation of the light source. Imatest offers a range of equipment for measuring uniformity.

To measure uniformity, think of the chart like a grid, and check the illuminance level in each grid square. Start by checking the center square, then each corner and each side. You may also check the illuminance levels at each key feature of the chart, such as the slanted-edge squares in the eSFR ISO test chart shown in Figure 3.

You should have no more than 20% variance in uniformity over the entire chart for SFR/MTF and distortion measurements, where small portions of the target are analyzed and exposure is not critical.

Software

If you do not have Imatest software installed, click here for detailed instructions on installing Imatest. For more information about Imatest software, see our licensing page.

Once Imatest is installed, instructions for getting started can be found here.

Direct image acquisition

Imatest supports direct acquisition from a wide range of frame grabbers and cameras as well as industry standard interfaces like CameraLink, GigE Vision, and USB through DirectShow (Windows) or QuickTime (OS X). Direct image acquisition cuts out several steps in the image quality testing process. Click here to learn more.